Perhaps you missed the point where they are 'neurally linked as one'. The trailers mentioned it briefly and so far we see them operating in synch because they are bridged. This is why they mentioned sharing memories, etc.

Even if that were possible, which it's not regardless of the level of technology, there's still no logical reason for it. There's no advantage to having two people neurally linked as one, while there would be countless disadvantages. If redundancy is a concern, then you have a backup pilot.